karamba - parametric structural analysis

Comment

Comment by Robert Vier on May 2, 2012 at 3:28am

Sorry Steven,

I didn't see you just set the 'WCompression' value different from zero. This indeed is kind of strange.

You can also set the weights to negative values, which means this section forces are 'even more avoided'.

Since I haven't written this latest version of FFF myself, I have to wait for my colleague to com e back next week for detailed discussion. But as soon as I have time I'll try to investigate the cause of this.

Best

Comment by Robert Vier on May 2, 2012 at 3:20am

Hello Steven!

Firstly, problem solving in general -be it with galapagos or our FFF-component - can be greatly eased by dividing a problem to sub-problems, e.g. using symmetries. If you divided you structure to four quarters, modeling just one of them with Rx,Ry,Rz and local-axe-Tx support conditions on the element-ends in the section planes (simulating the cut pieces of the structure), inherent symmetry is imposed. This also greatly increases performance with large structures.

Due to numeric inaccuracies, bot more due to the iterative incremental approach of FFF (where the number of elements to remove and elements to add in one iteration probably are not dividable by four in every iteration), symmetry is not always obtained. Either by splitting the model like described, or setting the parameters cleverly, you can avoid this.

Second, the karamba-manual http://www.food4rhino.com/project/karamba explaines the basic functionality of FFF-component and the meaning of the inputs.

The fact that it keeps working on the same element from approx. half of the process to the end in your example is explained as following: The 'Iter' -input specifies the number of iterations in which the structure is reduced to the specified 'Target'-mass-ratio, in your case 50. The remaining difference between 'MaxIter' and 'Iter', in your case 50, is used to 'smooth' the result by removing x elements (depending on 'Overdrive'-setting) and adding x elements again. The number of this smooting steps often can be reduced.

Your issue maybe also can be solved by increasing 'MinDist', which means that in one iteration only elements with a minimum distance of 'MinDist' between each other are processed.

'WLimit' specifies another 'smoothing'-value, which is a threshold-percentage of the average element weights. Elements weighted below this threshold will be removed.

Regarding the weights: In every step, each element is weighted by its average section forces:

W = SumOverAllSectionForces (Factor * AverageSectionForce)

The fact that tension elements remain with Tension-Factor set to zero probably is caused by specific structural situations where the element is e.g. much more needed for moments or shear and therefore remains in the system, though.

Hope I could help,

Best

Robert

Comment by Steven on May 2, 2012 at 2:23am

Hi there, I have been doing some structural optimisations using the Force Flow Finder component and I have a few questions about the results and the input parameters. A video of the optimisation I am working on can be found here:

https://vimeo.com/41407740

The script seems to generate very asymmetric results, which is unusual because the load is in the centre, and the supports are at the corners. After about 60 iterations it just keeps adding and removing the same member, but is clearly not at the most optimal solution.

I imagine it might be possible to tweak these results using the "Overdrive", "MinDist" and "WLimit" input parameters, but it is hard to understand exactly what these do and how they can be used to improve results. Could someone explain those to me?

Setting the tension input to 0 still yields members that are purely in tension, which also seems odd to me...

Thank you for your help!

Steven

Comment by David Shook on June 9, 2011 at 12:23am

There have been many great advancements.  Your work is very exciting.

Comment by karamba on June 7, 2011 at 9:06am

karamba 0.9.06 is out.

These are some of its new features:

- bi-directional evolutionary structural optimization (BESO)

- axial force and resultant moment per element

- bending- and axial deformation energy per element

- nodal displacements: translations and rotations

Comment by karamba on May 24, 2011 at 5:31am

There is no particular reason. I just thought that all the gha-files have to be in the 'Components'-folder of Grasshopper. Thank you for that tip!

Best,

Clemens

 

Comment by Jon Mirtschin on May 24, 2011 at 2:58am

Ok, thanks, I hadn't seen that the installer placed those dll's in that folder.

 

I typically have COFF loading unticked for my own plugins, if I relocate your gha file into the same folder as the dll's then it runs for me.  Is there a particular reason why you locate them in different folders?  

 

Thanks,  Jon

Comment by karamba on May 24, 2011 at 2:13am

Thank you very much David. We will add a note on our website and check the settings of the karamba-installer.

 

Jon: Maybe the 'karamba.dll' library can not be overwritten on some systems when a new version of karamba gets installed. This file is located in ''...\Rhinoceros 4.0\Plug-ins\Grasshopper". Try to remove it by hand and then run the installer.

 

Comment by Jon Mirtschin on May 23, 2011 at 11:32pm

Doesn't work for me, I still get a 

"Solution Exception, The type initializer for 'fem.karambaPINVOKE' threw an exception." in the analyze model component.

 

I have same software versions as you've listed.

Comment by David Shook on May 23, 2011 at 10:58pm

Ok.  Some success on getting the latest Karamba and GH running.  I have below.

Windows 7 (64-bit)

Rhino 4.0 SR9

GH 0.8.0010 (latest)

Karamba 0.9.05 (latest)

The key was to uninstall all GH and Karamba versions AND remove all relevant files from the below location: C:\Users\david.shook\AppData\Roaming\Grasshopper

Removing all files from the above location made the difference.

 

Karamba:  Please make some note of removing files from the above location on your website.  I think this is causing problems for Windows 7 users.

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